<template>
    <div class="list">
        <ul>
            <li class="item" 
                v-for="item in letters" 
                :key="item"
                :ref="item"
                @touchstart.prevent="handleTouchStart"
                @touchmove="handleTouchMove"
                @touchend="handleTouchEnd"
                @click="handleClick">
                {{item}}
            </li> 
        </ul>
    </div>
</template>

<script>
export default {
    name:"Alphabet",
    props:{
        cities:Object
    },
    data(){
        return{
            touchStatus:false
        }
    },
    computed:{
        letters(){
            const letters=[]
            for(let i in this.cities){ 
                letters.push(i)   
            }
            return letters
        },

        startY(){
           const startY=this.$refs['A'][0].offsetTop

           return startY
        }
    },
    methods:{
        handleClick:function(e){
            this.$emit('change',e.target.innerText)
        },
        handleTouchStart(){
            this.touchStatus=true
        },
        handleTouchMove(e){
            if(this.touchStatus){
               
               const touchY=e.touches[0].clientY-79
              
               const index=Math.floor((touchY-this.startY)/20)
               
               if(index>=0 && index<this.letters.length){
                    
                    this.$emit('change',this.letters[index])
               }
               
            }
        },
        handleTouchEnd(){
            this.touchStatus=false
        }
    }
}
</script>

<style lang="stylus" scoped>
  @import '~styles/varibles.styl'
  .list
    display: flex
    flex-direction: column
    justify-content: center
    position: absolute
    top: 1.58rem
    right: 0
    bottom: 0
    width: .4rem
    .item
      line-height: .4rem
      text-align: center
      color: $bgColor
        
</style>

